Association between daily 1‐km resolution levels of ambient air pollution and hospital visits for allergic diseases
Authors: Bi‐Xin He, Jia‐Jun Ma, He Lai, Chan‐Gu Li, Long‐Xin Huang, Hao‐Neng Huang, Xiao‐Qing Liu, Zhi‐Rou Zhou, Ying‐Chun Xie, Peng‐Peng Kuang, Chun‐Quan Ou, Qing‐Ling Fu
Journal: Allergy (2023)

Allergic diseases are extremely common disorders. Air pollutants may play an important role in inducing and exacerbating symptoms, resulting in significant increases in hospital visits.1, 2 Previous studies commonly evaluated the effects of ambient air pollutants on allergic diseases based on population-average exposure data by averaging the levels of air pollutants at several air-monitoring stations.3, 4 Biased effect estimates may occur in these studies, since spatial gradients and individual variations in exposure were not considered. Herein, we aimed to assess the effects of ambient air pollution on outpatient visits for allergic diseases using individual exposure data. Recently, we developed a model to accurately estimate the daily average fine particulate matter (PM2.5) and ozone (O3) at each of 1 km × 1-km grid in Mainland China.5 In this study, we extracted individual data of all outpatients visiting the Department of Allergy at the Second Affiliated Hospital of Guangzhou Medical University in 2014–2019. The grid-based level of ambient pollution was used as a proxy for the individual exposure of residents in this grid by matching patients' residential addresses to the grid data based on longitude and latitude (Figure 1A). The conditional logistic regression with a time-stratified case-crossover design was used to evaluate the effects of individual exposure to PM2.5 and O3. Since each case served as its own control and the referent days were very close to the case day (i.e. the date of the hospital visit) in this design, traditional confounding factors (e.g. sex and smoking) were well controlled. We also examined the effects of population-average exposure to pollutants (PM2.5, particulate matter [PM10], O3, nitrogen dioxide [NO2], sulphur dioxide [SO2] and carbon monoxide [CO]) using daily average levels of air pollution in 10 monitoring stations in Guangzhou. This study included a total of 16,647 outpatients with allergic diseases, mainly urticaria (35.5%), allergic rhinitis (22.4%), atopic dermatitis (9.2%) and asthma (2.8%). 57.46% of the cases were female, and 61.90% were aged <35 years (Table S1). The significant adverse impacts of individual exposure to PM2.5 and O3 occurred immediately on the current day and peaked the next day. A 10 μg/m3 increase in PM2.5 and O3 was associated with a 2.13% (95% CI: 0.63–3.65%) and 0.92% (95% CI: 0.16–1.67%) increase in the onset risk of allergic diseases on lag 0–1 day, respectively (Figure 1B). Additionally, we found that the population-average exposure to PM2.5, PM10, O3 and SO2 was associated with an increased risk of allergic diseases, with an excess risk of 1.43% (95% CI: 0.02–2.84%), 1.12% (95% CI: 0.10–2.95%), 1.10% (95% CI: 0.55–1.64%) and 9.98% (95% CI: 3.90–16.1%), respectively, while significant effect was not found for NO2 and CO (Table 1, Figure S1). This is the first study of the effects of daily exposure to PM2.5 and O3 on outpatient visits for allergic diseases based on satellite-retrieved grid-level pollution data at a 1-km resolution. Using monitoring pollution data confirmed the results but with slightly different effect estimates. Only one previous study investigated the effects of PM2.5 at 10 km × 10-km resolution on allergic diseases in preschool children of six Chinese cities based on the Global Burden of Disease project.6 Patients' exposure levels were authentically reflected by grid-level data in our study, which can greatly reduce exposure measurement error and bias in the impact estimates of air pollution. The impacts of air pollution may vary for different allergic diseases. Unfortunately, the statistically significant effect on specific allergic diseases was not detected in this single-hospital study, which might be due to low statistical power with insufficient sample size. Subgroup analysis showed that patients aged 35–64 years were significantly more sensitive to O3 and PM2.5, probably because of a higher likelihood of outdoor work (Table S2). In conclusion, this study highlights the adverse effects of PM2.5 and O3 on allergic diseases. Additionally, exposure to ambient SO2 and PM10 are associated with an increased risk of allergic diseases. These findings support efforts to mitigate ambient air pollution and protect people susceptible to allergens by recommending safety limitations. Qing-Ling Fu and Chun-Quan Ou initiated this study. Bi-Xin He, He Lai, Chan-Gu Li, Long-Xin Huang, Xiao-Qing Liu, Zhi-Rou Zhou, Ying-Chun Xie and Peng-Peng Kuang helped in the data collection. Jia-Jun Ma and Hao-Neng Huang analysed the data. Bi-Xin He, Jia-Jun Ma, Qing-Ling Fu and Chun-Quan Ou contributed to the manuscript writing. Qing-Ling Fu and Chun-Quan Ou helped in final approval of the manuscript. We thank the Second Affiliated Hospital of Guangzhou Medical University for the cooperation. This work was supported by grants from National Natural Science Foundation of China (No. 82271144, No. 81970863 to Qing-Ling Fu and No. 81573249 to Chun-Quan Ou) and Guangzhou Key R&D Program (2023B03J1233). All authors declare no conflict of interest regarding the publication of this article. The data that support the findings of this study are available from the corresponding author upon reasonable request. Data S1: Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.